# Coffee Machine Desgin help PLEASE

Hey Everyone, Not sure if this is where I can post this topic. I have a project in class to design a 10cent coffee machine. We just have to create the truth table, write the SOP form. Draw the circuit on @ltera and program the CPLD. I am having trouble creating the truth table, I know the inputs are N1(Nickel 1), N2(Nickel 2), D(Dime), Q(Quarter). The coffee machine has to give back the correct change so I know the outputs are C(coffee), N(Nickel), D1(Dime1), D2(Dime2), Q(Quarter). This is the start of my truth table.
_____INPUTS_________________OUTPUTS______
N1__N2__D___Q __________C___N__D1__D2__Q
0___0___0____0___________0___0___0___0___0
0___0___0____1___________1___1___1___0___0

Since I only have 4 inputs there should only be 16 possible combinations right? I get confused when you get the truth table and reduce the boolean sum of products for all five outputs. I am not sure if my equation is correct and I think I made a mistake on my truth table. Can anyone help me on the correct truth table to the design on this machine? Thanks guys

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DaveC426913
Gold Member
Where exactly are you having trouble?

Do you know what the next line is?

yeah the whole truth table I got is

_____INPUTS_________________OUTPUTS______
N1__N2__D___Q __________C___N__D1__D2__Q
0___0___0____0___________0___0___0___0___0
0___0___0____1___________1___1___1___0___0
0___0___1____0___________1___0___0___0___0
0___0___1____1___________1___0___0___0___1
0___1___0____0___________0___1___0___0___0
0___1___0____1___________1___0___1___1___0
0___1___1____0___________1___1___0___0___0
0___1___1____1___________1___1___0___0___1
1___0___0____0___________0___1___0___0___0
1___0___0____1___________1___0___1___1___0
1___0___1____0___________1___1___0___0___0
1___0___1____1___________1___1___0___0___1
1___1___0____0___________1___0___0___0___0
1___1___0____1___________1___0___0___0___1
1___1___1____0___________1___0___1___0___0
1___1___1____1___________1___0___1___0___1

I wanted to be sure that this was the correct truth table for the design of a 10cent coffee machine that accepts 2 nickels, a dime, a quarter or any combination of those 4. AND also gives change for any amount over 10cents. I am having trouble writing the SOP forum of each output. I got the SOP for each output and then I used altera to test the circuit and it dosent go with this truth table. So I think I messed up somewhere on the table or writing the SOP forums of each output. Can anyone verify this is the correct table for my design? and the SOP forum for each output?

Entered by truthtable:
C = N1' N2' D' Q + N1' N2' D Q' + N1' N2' D Q + N1' N2 D' Q + N1' N2 D Q' + N1' N2 D Q + N1 N2' D' Q + N1 N2' D Q' + N1 N2' D Q + N1 N2 D' Q' + N1 N2 D' Q + N1 N2 D Q' + N1 N2 D Q;
N = N1' N2' D' Q + N1' N2 D' Q' + N1' N2 D Q' + N1' N2 D Q + N1 N2' D' Q' + N1 N2' D Q' + N1 N2' D Q;
D1 = N1' N2' D' Q + N1' N2 D' Q + N1 N2' D' Q + N1 N2 D Q' + N1 N2 D Q;
D2 = N1' N2 D' Q + N1 N2' D' Q;
Q1 = N1' N2' D Q + N1' N2 D Q + N1 N2' D Q + N1 N2 D' Q + N1 N2 D Q;

Minimized:
C = N1 N2' D' Q + N1' N2 D' Q + N1' N2' D' Q + N1 N2 + D ;
N = N1 N2' Q' + N1' N2 Q' + N1' N2' D' Q + N1 N2' D + N1' N2 D ;
D1 = N1 N2' D' Q + N1' N2 D' Q + N1' N2' D' Q + N1 N2 D ;
D2 = N1 N2' D' Q + N1' N2 D' Q;
Q1 = N1 N2 Q + D Q;

Minimized Product of Sums:
C = (N1+D+Q)(N2+D+Q);
N = (N1'+N2')(N1+N2+Q)(N1+N2+D')(N1+N2'+D+Q')(N1'+N2+D+Q');
D1 = (N1+D')(N2+D')(N1+D+Q)(N2+D+Q)(N1'+N2'+D);
D2 = (Q)(N1+D')(N2+D')(N1'+N2')(N1+N2+D);
Q1 = (Q)(N1+N2+D)(N1+N2'+D+Q')(N1'+N2+D+Q');

Factored:
C = D' Q (N2' (N1' + N1) + N1' N2) + N1 N2 + D;
N = N1' N2' D' Q + (N1 N2' + N1' N2) (Q' + D);
D1 = D' Q (N2' (N1' + N1) + N1' N2) + N1 N2 D;
D2 = D' Q (N1 N2' + N1' N2);
Q1 = Q (N1 N2 + D);

Can anyone see what I am doing wrong? or if this equation works for the design I am trying to create? I don't have the equipment at home to test this circuit. Thanks any help is appreciated

Last edited:
DaveC426913
Gold Member